Estimating Nurses' Exposures to Ionizing Radiation: The Elusive Gold Standard

Abstract

This study assessed ionizing radiation exposure in 58,125 registered nurses in British Columbia, Canada, for a cohort study of cancer morbidity and mortality. Two methods were used: (1) a survey of nurses in more than 100 acute care hospitals and health care centers; (2) and monitoring data reported to the National Dose Registry of Health Canada, considered the gold standard. The mean exposure of cohort nurses monitored during the study period from 1974 to 2000 was 0.27 milliSieverts (7028 person-years of monitoring). Of 609,809 person-years in the cohort, 554,595 (90.9%) were identified as unexposed by both exposure assessment methods. Despite crude agreement of 91% between the methods, weighted kappa for agreement beyond chance was only 0.045, and the sensitivity of the survey method to capture National Dose Registry monitored person-years was only 0.085 (specificity = 0.97). The survey missed exposures outside the acute care setting. The National Dose Registry also missed potential exposures, especially among hospital emergency department and pediatric staff nurses. It was unlikely that either method estimated nurses' true exposures to ionizing radiation with good sensitivity and specificity. The difficulty in exposure assessment likely arises because fewer than 10% of registered nurses are exposed to ionizing radiation, yet the settings in which they are exposed vary tremendously. This means that careful hazard assessment is required to ensure that monitoring is complete where exposures are probable, without incurring the excess costs and lack of specificity of including the unexposed.

Keywords:

• dosimetry
• epidemiology
• ionizing radiation
• occupational exposures

ACKNOWLEDGMENTS

The authors are grateful to all the nurses who participated in the survey design and administration for their helpful cooperation; the College of Registered Nurses of British Columbia for providing the cohort register; Willem Sont and Pat Ashmore of the National Dose Registry for the opportunity to link the Registry data to the cohort and for their explanations of the data; Statistics Canada for performing the linkage; and Leila Shobab, Lindsay Graham, and Elisa Murru for assistance in the administration of the survey. This study was funded in part by the Research Secretariat of WorkSafeBC.

Notes

^A All geometric means are less than the detection limit of 0.20 mSv, since 78% of measurements were below detection limits; the geometric means were calculated values after substitution of 0.0143 mSv for all values less than the detection limit.